[Android] Handle a null java side of CVC in context menu

chrome/browser/ui/android/context_menu_helper.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/android/context_menu_helper.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "content/public/browser/android/content_view_core.h"
 #include "content/public/browser/android/download_controller_android.h"
@@ skipping 23 matching lines @@
 }
 
 void ContextMenuHelper::ShowContextMenu(
     const content::ContextMenuParams& params) {
   content::ContentViewCore* content_view_core =
       content::ContentViewCore::FromWebContents(web_contents_);
 
   if (!content_view_core)
     return;
 
+  base::android::ScopedJavaLocalRef<jobject> jcontent_view_core(
+      content_view_core->GetJavaObject());
+
+  if (jcontent_view_core.is_null())
+    return;
+
   JNIEnv* env = base::android::AttachCurrentThread();
   context_menu_params_ = params;
   Java_ContextMenuHelper_showContextMenu(
       env,
       java_obj_.obj(),
-      content_view_core->GetJavaObject().obj(),
+      jcontent_view_core.obj(),
       ContextMenuHelper::CreateJavaContextMenuParams(params).obj());
 }
 
 // Called to show a custom context menu. Used by the NTP.
 void ContextMenuHelper::ShowCustomContextMenu(
     const content::ContextMenuParams& params,
     const base::Callback<void(int)>& callback) {
   context_menu_callback_ = callback;
   ShowContextMenu(params);
 }
@@ skipping 50 matching lines @@
   content::DownloadControllerAndroid::Get()->StartContextMenuDownload(
       context_menu_params_,
       web_contents_,
       jis_link);
 }
 
 bool RegisterContextMenuHelper(JNIEnv* env) {
   return RegisterNativesImpl(env) &&
          ContextMenuParamsAndroid::RegisterNativesImpl(env);
 }